Browse Articles

Widening of the tropics in global surface-air winds

Nuclear quantum effects in condensed phase: The case of the “association band” of liquid water

The combination band just above 2000 cm−1 appearing in the infrared spectrum of liquid water is well known from experiments, and it is thought to originate from the combination of bending motions of the water molecules and the large-amplitude libration modes of the condensed phase. While classical simulations cannot genuinely reproduce this band, here we show that this exquisitely quantum signal can be simulated by on-the-fly ab initio semiclassical molecular dynamics. The number of atoms involved in reproducing this combination band, which is also known as the “association band” of liquid water, shows that this condensed phase signal is quite local.

Lipid remodeling and circulating semaphorin 3A in diminished ovarian reserve

Computing nonequilibrium transport from short-time transients: From Lorentz gas to heat conduction in one-dimensional chains

We test the Transient Time Correlation Function (TTCF) method to compute nonequilibrium transport coefficients, highlighting its conceptual and practical differences from the standard time-average approach. While time averages extract transport properties from long stationary trajectories and discard transient dynamics, TTCF adopts the complementary strategy: it exploits the information contained in short-time transients following the onset of an external perturbation while discarding the long-time evolution once stationarity is reached. We revisit the theoretical framework of TTCF and assess its numerical performance through representative case studies: the Lorentz gas and a many-body system, namely, a chain of oscillators with an anharmonic pinning potential. By direct comparison with time averages, we show that for the Lorentz gas, TTCF yields consistent transport coefficients in both linear and nonlinear regimes at a reduced computational cost. Moreover, TTCF displays superior precision in the linear-response regime and remains reliable in nonergodic situations, revealing the presence of regions of phase space corresponding to different behaviors, as well as the possibility of phase transitions. For the anharmonic chain, we show that TTCF is a scalable and efficient alternative for the numerical study of nonequilibrium transport.

Clinical characteristics, disease activity and psychosocial burden of axial spondyloarthritis in Jordan: a multicenter cross-sectional study

Open-boundary molecular dynamics of red blood cell suspensions

Blood is a complex suspension of deformable red blood cells (RBCs), and its rheology plays a central role in physiology and pathology. While many computational studies have examined hemorheology under periodic or wall-confined flows, these approaches cannot capture the exchange of mass, momentum, and energy with the surroundings, a feature essential for the realistic simulation of non-equilibrium processes. Open-boundary methods provide this capability but remain largely underexplored. We present the first application of open-boundary molecular dynamics (OBMD) to RBC suspensions, with explicit control of flux exchange across the open boundary. The framework combines dissipative particle dynamics for the solvent and a coarse-grained RBC membrane model and introduces a novel, efficient membrane insertion algorithm capable of handling high hematocrits. It reproduces experimental bulk hemorheological properties, including shear-thinning and hematocrit-dependent viscosity. Our results validate OBMD for modeling blood rheology and establish a computational foundation for future studies of ultrasound–blood interactions and other phenomena where periodic boundaries constrain natural dynamics, such as pressure-driven flows, transient inflows, and cell-free layer formation.

Research on the impact of diversity in financial ecosystems on new energy systems

The geometric control of boundary-catalytic branching processes

Boundary-catalytic branching processes describe a broad class of natural phenomena where the population of diffusing particles grows due to their spontaneous binary branching (e.g., division, fission, or splitting) on a catalytic boundary located in a complex environment. We investigate the possibility of the geometric control of the population growth by compensating for the proliferation of particles due to catalytic branching events by their absorptions in the bulk or on absorbing regions of the boundary. We identify an appropriate Steklov spectral problem to obtain the phase diagram of this out-of-equilibrium stochastic process. The principal eigenvalue determines the critical line that separates an exponential growth of the population from its extinction in a bounded domain. In other words, we establish a powerful tool for calculating the optimal absorption rate that equilibrates the opposite effects of branching and absorption events and, thus, results in steady-state behavior of this diffusion–reaction system. Moreover, we show the existence of a critical catalytic rate above which no compensation is possible, so that the population cannot be controlled and keeps growing exponentially. The proposed framework opens promising perspectives for better understanding, modeling, and control of various boundary-catalytic branching processes, with applications in physics, chemistry, and life sciences.

The impact of junk food on male fertility in mice: therapeutic interventions targeting advanced glycation end-products and oxidative stress

Symmetry-controlled ultrastrong phonon–photon coupling in a terahertz cavity

Optical cavities provide a powerful means to engineer light–matter hybrid states by coupling confined electromagnetic fields with matter excitations. Achieving in situ control of the coupling strength is essential for investigating how such hybridization evolves with the coupling strength. In this work, we use a symmetry-changing structural phase transition in lead halide perovskites to reversibly tune the phonon–photon coupling strength, leveraging the fact that their phonon frequencies and oscillator strengths are dictated by lattice symmetry. Terahertz time-domain spectroscopy of MAPbI3 embedded in nanoslot cavities reveals three polariton branches above the critical temperature Tc ≃ 162.5 K and the emergence of an additional branch below Tc, activated by a new phonon mode in the low-temperature phase. The full dispersion is accurately reproduced using a multimode Hopfield model, confirming that all normalized coupling strengths remain in the ultrastrong coupling regime. These results demonstrate symmetry-controlled tuning of ultrastrong light–matter coupling in optical cavities via temperature.

An interpretable IGWO-MKRVM model for predicting excavation damaged zone thickness of drift

Seniority-zero linear canonical transformation theory

We propose a method to solve the electronic Schrödinger equation for strongly correlated systems by applying a unitary transformation to reduce the complexity of the physical Hamiltonian. In particular, we seek a transformation that maps the Hamiltonian into the seniority-zero space: seniority-zero wavefunctions are computationally simpler, but still capture strong correlation within electron pairs. The unitary rotation is evaluated using the Baker–Campbell–Hausdorff expansion, truncated to two-body operators through the operator decomposition strategy of canonical transformation (CT) theory, which rewrites higher-rank terms approximately in terms of one- and two-body operators. Unlike conventional approaches to CT theory, the generator is chosen to minimize the size of non-seniority-zero elements of the transformed Hamiltonian. Numerical tests reveal that this Seniority-zero Linear Canonical Transformation (SZ-LCT) method delivers highly accurate results, usually with sub-milliHartree error. The effective computational scaling of SZ-LCT is O(N8/nc), where nc is the number of cores available for the computation.

Tuning the electronic and electrochemical properties of 2D SiC by defect insertion for next-generation metal-ion battery anodes: first principles prediction

Vibrational mode specificity in H + NHD2 → H2 + ND2: A full-dimensional quantum dynamics study

The vibrational mode specificity in the polyatomic reaction H + NHD2 → H2 + ND2 is investigated using full-dimensional quantum dynamics calculations. Using a mixed Jacobi/Radau coordinate system, we perform time-dependent wave packet calculations to explore how different vibrational excitations of the NHD2 reactant influence reaction probabilities and integral cross sections. This study reveals that specific vibrational modes, particularly the umbrella mode and the N–H stretching mode, significantly enhance reactivity by directly coupling with the reaction coordinate. In contrast, vibrational excitations localized on the non-reactive ND2 group exert minimal effects. Notably, the umbrella mode’s tunneling splitting leads to distinct dynamics for its two components, with higher excitation states showing complex energy-dependent behavior. These findings highlight the critical role of mode-specific vibrational excitations in polyatomic reaction dynamics and underscore the necessity of accurate full-dimensional quantum calculations for elucidating complex reaction mechanisms.

Exploring quantum Heider balance theory

Glycerol and propylene glycol nucleation in a laminar flow diffusion chamber

Homogeneous nucleation enables aerosol generation from supersaturated vapors. Despite extensive vapor-phase nucleation research, quantitative data on nucleation rates for specific substances and their mixtures remain limited. This study investigates the homogeneous nucleation of glycerol and propylene glycol using a laminar flow diffusion chamber at three saturator temperatures. Experimental nucleation rates were derived from the measured particle concentrations and normalized using computational fluid dynamics modeling based on the classical nucleation theory. Simulations were employed to resolve temperature and saturation ratio profiles, enabling accurate reconstruction of nucleation isotherms. Findings agree with prior diffusion cloud chamber studies and were further evaluated using Hale plot scaling. Results show that the nucleation of propylene glycol occurs at significantly lower supersaturation and smaller temperature gradients between the saturator and condenser compared to glycerol. Critical cluster sizes were determined both from the Kelvin equation and from the slopes of nucleation isotherms, revealing that glycerol forms smaller critical clusters (0.72–0.97 nm) than propylene glycol (1.3–1.5 nm). These findings align with previously reported results obtained using diffusion cloud chambers and confirm the influence of molecular structure on nucleation behavior. This study provides valuable insight into the fundamental nucleation mechanisms of polyhydroxylated compounds and supports the design and optimization of aerosol-forming processes in practical applications.

Gravitational effects on the hydrogen bond network of water and ionic solutions revealed by near infrared spectroscopy under simulated microgravity

Abstract The near-infrared spectra of ultrapure water and five types of ionic aqueous solutions were recorded under normal and simulated microgravity (< 0.1 G). The water band at approximately 1450 nm, corresponding to the combination of O–H symmetric and antisymmetric stretching vibrations, was analyzed. The results showed that the hydrogen-bond network (HBN) weakened in both ultrapure water and all ionic solutions under microgravity. This weakening is physically reasonable when considered in terms of a slight decrease in hydrostatic pressure leading to volumetric expansion of water. Furthermore, weakening of the HBN by gravity changes was smaller than that caused by modest temperature changes of approximately 2 °C and varied depending on the type of ions present. Specifically, gravity-induced changes in the HBN of water were less pronounced in solutions containing kosmotropic anions than in solutions containing chaotropic anions. These findings suggest that even subtle changes in HBN could disrupt finely tuned biochemical reactions, potentially influencing human health in altered gravity environments.

Water–ice III interfacial free energy: A mold integration study using the TIP4P/Ice model

In this work, we evaluate the interfacial free energy, γ, between ice III and liquid water along the coexistence line for the TIP4P/Ice model using the mold integration technique. The calculated γ values exceed 40 mJ/m2 across all the studied pressures. We observe a non-monotonic pressure dependence with a minimum appearing near 4000 bar, analogously to that observed for hexagonal ice at negative pressures. Furthermore, the interfacial free energy was determined for two different crystal planes at one pressure, revealing an anisotropy of less than 1%.

Value of transcranial color-coded duplex sonography-derived middle cerebral artery pulsatility index in intracranial pressure assessment at moderate to high altitudes

Vibrational relaxation of D2O by collisions with Ar atoms

Vibrational relaxation of D2O(v2, v13) molecules by collisions with Ar atoms was studied at 298 K (v2 denotes the bending vibrational mode and v13 denotes the collisionally coupled v1 and v3 stretching modes). The vibrationally excited D2O molecules were generated in two ways: exothermic abstraction reactions of OD radicals with different RD reactants and unimolecular decomposition of chemically activated compounds. The D2O(v2, v13) distributions were observed by infrared emission from a fast-flow reactor as a function of Ar pressure and reaction time. State-specific relaxation rate constants were obtained by comparison of the time evolution of the experimental vibrational distributions with numerical kinetic calculations of the vibrational populations. The relaxation mechanism was based on the relaxation model of H2O studied earlier, with the addition of a few channels specific for D2O. The average rate constants of the loss of population from (01), (02), (03), and (04) stretching states are (1.2 ± 0.2) × 10−14, (2.8 ± 0.6) × 10−14, (5.3 ± 0.8) × 10−14, and (11.3 ± 2.2) × 10−14 cm3 molecule−1 s−1, respectively. A rate constant of (3.9 ± 0.9) × 10−14 cm3 molecule−1 s−1 was assigned to the relaxation of the first level (v2 = 1, v13 = 0), which is in agreement with two other measurements. The rate constants of higher bending states increase linearly with the v2 quantum number and decrease slightly as v13 increases from v13 = 0 to v13 = 1–3. In general, the rate constants for the relaxation of D2O(v2,v13) are 3–5 times smaller than those for H2O(v2, v13) reported in an earlier study, despite the smaller energy defects for D2O. Our results for D2O and H2O relaxation by collisions with Ar are compared with existing experimental studies and theoretical models.